I have a 1988 Merc 9.9 that is difficult to start when cold and looses power past 1/4 throttle. With max. idle and choke engaged it takes 3 to 4 pulls to start when cold. When running cold it runs rough and the RPM decreases and it stalls. This is repeated 3 or 4 times until engine warms up. When it is finally warm it idles fine. From this point shifting to forward and cruising at 1/4 throttle all day would be no problem. Once I try and go beyond that the engine goes through a series of forward lurches and power loss cycles or it just bogs down and stalls if I give it to much gas. Restarting the engine when warm takes one pull but still has the loss of power issue. I have replaced the spark plugs, fuel and fuel filter. There are no visible leaks in the fuel lines and no debris in the tank and screen and the choke mechanism seems to be functioning. Any ideas on where to go from here would be appreciated.

Sounds like your carburetor needs to be cleaned and rebuilt. Make sure after the carb is serviced to use brand new gas with no contamiation.